Los Angeles police officers remove an Occupy protester from the camp at the City Hall. Photograph: Bret Hartman/EPA

Los Angeles police used nearly a dozen undercover detectives to infiltrate the Occupy LA encampment before this week's raid to gather information on the anti-Wall Street protesters' intentions, according to media reports.

None of the officers slept at the camp, but they tried to blend in during the weeks leading up to the raid to learn about plans to resist or use weapons against police, a police source told the Los Angeles Times. The source spoke on the condition of anonymity because the case is ongoing.

The undercover work yielded information that some protesters were preparing bamboo spears and other potentially dangerous weapons in advance of an expected eviction, none of which were used, according to the City News Service, which first reported the story.

Police played down the significance of the undercover work since Occupy meetings were public and easily tracked.